The structure of smooth muscle myosin light chain kinase is being investigated. Using selective proteolysis, we are studying the sites phosphorylated by the cAMP-dependent protein kinase and the calmodulin binding domain of myosin light chain kinase. We are also interested in the generation of active subfragments of myosin light chain kinase which to longer require the presence of calcium, calmodulin and are no longer regulated by phosphorylation.